Aggressively Expanding Civilizations

Ever since I became an environmentalist, the potential destruction wrought by aggressively expanding civilizations has been haunting my thoughts. Not just here and now, where it’s easy to see, but in the future.

A long time ago on this diary, I mentioned my friend Bruce Smith’s nightmare scenario. In the quest for ever faster growth, corporations evolve toward ever faster exploitation of natural resources. The Earth is not enough. So, ultimately, they send out self-replicating von Neumann probes that eat up solar systems as they go, turning the planets into more probes. Different brands of probes will compete among each other, evolving toward ever faster expansion. Eventually, the winners will form a wave expanding outwards at nearly the speed of light—demolishing everything behind them, leaving only wreckage.

The scary part is that even if we don’t let this happen, some other civilization might.

The last point is the key one. Even if something is unlikely, in a sufficiently large universe it will happen, as long as it’s possible. And then it will perpetuate itself, as long as it’s evolutionarily fit. Our universe seems pretty darn big. So, even if a given strategy is hard to find, if it’s a winning strategy it will get played somewhere.

So, even in this nightmare scenario of "spheres of von Neumann probes expanding at near lightspeed", we don’t need to worry about a bleak future for the universe as a whole—any more than we need to worry that viruses will completely kill off all higher life forms. Some fraction of civilizations will probably develop defenses in time to repel the onslaught of these expanding spheres.

It’s not something I stay awake worrying about, but it’s a depressingly plausible possibility. As you can see, I was trying to reassure myself that everything would be okay, or at least acceptable, in the long run.

Even earlier, S. Jay Olson and I wrote a paper together on the limitations in accurately measuring distances caused by quantum gravity. If you try to measure a distance too accurately, you’ll need to concentrate so much energy in such a small space that you’ll create a black hole!

That was in 2002. Later I lost touch with him. But now I’m happy to discover that he’s doing interesting work on quantum gravity and quantum information processing! He is now at Boise State University in Idaho, his home state.

Expanding bubbles

What will happen if some civilizations start aggressively expanding through the Universe at a reasonable fraction of the speed of light? We don’t have to assume most of them do. Indeed, there can’t be too many, or they’d already be here! More precisely, the density of such civilizations must be low at the present time. The number of them could be infinite, since space is apparently infinite. But none have reached us. We may eventually become such a civilization, but we’re not one yet.

Each such civilization will form a growing ‘bubble’: an expanding sphere of influence. And occasionally, these bubbles will collide!

Here are some pictures from a simulation he did:

As he notes, the math of these bubbles has already been studied by researchers interested in inflationary cosmology, like Alan Guth. These folks have considered the possibility that in the very early Universe, most of space was filled with a ‘false vacuum’: a state of matter that resembles the actual vacuum, but has higher energy density.

A false vacuum could turn into the true vacuum, liberating energy in the form of particle-antiparticle pairs. However, it might not do this instantly! It might be ‘metastable’, like ball number 1 in this picture:

It might need a nudge to ‘roll over the hill’ (metaphorically) and down into the lower-energy state corresponding to the true vacuum, shown as ball number 3. Or, thanks to quantum mechanics, it might ‘tunnel’ through this hill.

The balls and the hill are just an analogy. What I mean is that the false vacuum might need to go through a stage of having even higher energy density before it could turn into the true vacuum. Random fluctuations, either quantum-mechanical or thermal, could make this happen. Such a random fluctuation could happen in one location, forming a ‘bubble’ of true vacuum that—under certain conditions—would rapidly expand.

It’s actually not very different from bubbles of steam forming in superheated water!

But here’s the really interesting Jay Olson noted in his first paper on this subject. Research on bubbles in the inflationary cosmology could actually be relevant to aggressively expanding civilizations!

Why? Just as a bubble of expanding true vacuum has different pressure than the false vacuum surrounding it, the same might be true for an aggressively expanding civilization. If they are serious about expanding rapidly, they may convert a lot of matter into radiation to power their expansion. And while energy is conserved in this process, the pressure of radiation in space is a lot bigger than the pressure of matter, which is almost zero.

General relativity says that energy density slows the expansion of the Universe. But also—and this is probably less well-known among nonphysicists—it says that pressure has a similar effect. Also, as the Universe expands, the energy density and pressure of radiation drops at a different rate than the energy density of matter.

So, the expansion of the Universe itself, on a very large scale, could be affected by aggressively expanding civilizations!

The fun part is that Jay Olson actually studies this in a quantitative way, making some guesses about the numbers involved. Of course there’s a huge amount of uncertainty in all matters concerning aggressively expanding high-tech civilizations, so he actually considers a wide range of possible numbers. But if we assume a civilization turns a large fraction of matter into radiation, the effects could be significant!

The effect of the extra pressure due to radiation would be to temporarily slow the expansion of the Universe. But the expansion would not be stopped. The radiation will gradually thin out. So eventually, dark energy—which has negative pressure, and does not thin out as the Universe expands—will win. Then the Universe will expand exponentially, as it is already beginning to do now.

(Here I am ignoring speculative theories where dark energy has properties that change dramatically over time.)

Jay Olson’s work

Here are his papers on this subject. The abstracts sketch his results, but you have to look at the papers to see how nice they are. He’s thought quite carefully about these things.

Abstract. In the context of a homogeneous universe, we note that the appearance of aggressively expanding advanced life is geometrically similar to the process of nucleation and bubble growth in a first-order cosmological phase transition. We exploit this similarity to describe the dynamics of life saturating the universe on a cosmic scale, adapting the phase transition model to incorporate probability distributions of expansion and resource consumption strategies. Through a series of numerical solutions spanning several orders of magnitude in the input assumption parameters, the resulting cosmological model is used to address basic questions related to the intergalactic spreading of life, dealing with issues such as timescales, observability, competition between strategies, and first-mover advantage. Finally, we examine physical effects on the universe itself, such as reheating and the backreaction on the evolution of the scale factor, if such life is able to control and convert a significant fraction of the available pressureless matter into radiation. We conclude that the existence of life, if certain advanced technologies are practical, could have a significant influence on the future large-scale evolution of the universe.

Abstract. If advanced civilizations appear in the universe with a desire to expand, the entire universe can become saturated with life on a short timescale, even if such expanders appear but rarely. Our presence in an untouched Milky Way thus constrains the appearance rate of galaxy-spanning Kardashev type III (K3) civilizations, if it is assumed that some fraction of K3 civilizations will continue their expansion at intergalactic distances. We use this constraint to estimate the appearance rate of K3 civilizations for 81 cosmological scenarios by specifying the extent to which humanity could be a statistical outlier. We find that in nearly all plausible scenarios, the distance to the nearest visible K3 is cosmological. In searches where the observable range is limited, we also find that the most likely detections tend to be expanding civilizations who have entered the observable range from farther away. An observation of K3 clusters is thus more likely than isolated K3 galaxies.

Abstract. If a subset of advanced civilizations in the universe choose to rapidly expand into unoccupied space, these civilizations would have the opportunity to grow to a cosmological scale over the course of billions of years. If such life also makes observable changes to the galaxies they inhabit, then it is possible that vast domains of life-saturated galaxies could be visible from the Earth. Here, we describe the shape and angular size of these domains as viewed from the Earth, and calculate median visible sizes for a variety of scenarios. We also calculate the total fraction of the sky that should be covered by at least one domain. In each of the 27 scenarios we examine, the median angular size of the nearest domain is within an order of magnitude of a percent of the whole celestial sphere. Observing such a domain would likely require an analysis of galaxies on the order of a giga-lightyear from the Earth.

Here are the main assumptions in his first paper:

1. At early times (relative to the appearance of life), the universe is described by the standard cosmology – a benchmark Friedmann-Robertson-Walker (FRW) solution.

2. The limits of technology will allow for self-reproducing spacecraft, sustained relativistic travel over cosmological distances, and an efficient process to convert baryonic matter into radiation.

3. Control of resources in the universe will tend to be dominated by civilizations that adopt a strategy of aggressive expansion (defined as a frontier which expands at a large fraction of the speed of the individual spacecraft involved), rather than those expanding diffusively due to the conventional pressures of population dynamics.

4. The appearance of aggressively expanding life in the universe is a spatially random event and occurs at some specified, model-dependent rate.

5. Aggressive expanders will tend to expand in all directions unless constrained by the presence of other civilizations, will attempt to gain control of as much matter as is locally available for their use, and once established in a region of space, will consume mass as an energy source (converting it to radiation) at some specified, model-dependent rate.

I loved science fiction when I was young. Now I wonder if the fact that we have not yet been “visited” or attacked might actually be evidence that the light-speed barrier is not particularly easy to crack.

Yes. And if one could break the light-speed barrier, with special relativity remaining roughly correct, one should also be able to travel ‘backwards in time’. That is, if we fix a frame of reference, we could get from a point at time to a point at some earlier time a distance away as long as

where is the speed of light. So, very faraway civilizations could reach us even starting from the future.

You certainly have some interesting friends John. For anyone who has read the second and third papers – are there enough specifics to form the basis for a program of observation or data-mining based on Jay’s analyses?

The second and third papers are written with that in mind. IF these things are out there and IF they are visible (they are not likely to be visible in scenarios where they expand sufficiently fast, for example), most plausible scenarios seem to have two generic features in common — the closest domains are likely to be very far away (billions of light years), and they are likely to eclipse a large region of the sky (a solid angle perhaps a thousand times the size of the moon).

However, one still needs to know how to identify a life-saturated galaxy when one sees it. People have already looked at nearby galaxies for excess waste heat in the mid-IR, for example, but perhaps there are other things one could look for as well.

I am thinking that a galaxy color-magnitude diagram can be useful to search aggressively expanding civilization: if there is a civilization, then there is a change in the emission, and there is a displacement in the underpopulated space (the green valley); so that an automatic search in the emission spectrum can give a measure of radio emission of a possible civilization; even there is not total occupation, there is a possible observable effect.
it is easier than trying inhabited planets.

Human imagination is unlimited, which is not at all like actual reality, which has lots of limitations. It’s the reason why reality has Laws and imagination does not. For example, the Law of Conservation of Mass/Energy is a limitation of the amount of mass/energy in a system. It’s why imaginary stories of perpetual motion of the third kind are not possible in real life.

An aggressively expanding civilization does not reflect reality in the least. It reminds me of the majority of sci-fi monster movies, which have no possibility whatsoever of being possible in any Universe, except an imaginary one. Take Prometheus for example. The sterile Elizabeth Shaw gets pregnant with an alien, has it surgically removed, and abandons the alien fetus in the very sterile, and not very big operating room. A few days later she returns to find the fetus has turned into a huge, multi-ton adult. What we see of the room is pristine. So what did the alien feed on to become that huge? The alien would have had to eat multi-tons of something in order to gain multi-tons of weight. And where did the additional multi-ton amounts of waste products it produce, go to?

Likewise, an aggressively expanding civilization would violate just as many numerous Laws of physics and thermodynamics as the alien in Prometheus did…heck! Even simple math would be violated in order to imagine such a civilization, since there needs to be a simple balance between consumption of energy/matter and it’s usage, especially at light speeds, which requires an infinite amount of energy for matter with mass to achieve, and which the imaginary civilization has no trouble doing. Interesting how humans can imagine a civilization that exists, that is not physically possible in the real life world, yet they can go into great details, mathematically and physically, of how it functions and how it relates to real life. They believe they can use imaginary things to know how real life things work, never imagining that this kind of “thinking” is not logical.

But let’s talk about this from a scientific perspective — the psychological one to be more specific. People try to imagine that there are alien civilizations out there that could aggressively take over the Universe and ruin it. This is called a psychological “projection”. It represents the idea that people know they (not aliens) are ruining but the Earth (not the Universe). They know that our civilization is aggressively consuming Earth’s limited resources with a seemingly unlimited population growth, but rather than face these facts and do something logical about it, they project it into a storytale and do nothing but talk about it.

In real life, a civilization that thinks only in terms of its own survival without any regard for other life or the balance of nature or other life forms, is a civilization doomed for extinction, as humans are just now painfully becoming aware of. Too bad humans aren’t as smart as they imagine themselves to be, because they are starting to come to this realization too late to do anything significant about it at this point in time.

Some people like to say, “what goes around, comes around” and humans most certainly deserve to have happen to them, the same horrible things they’ve been doing to this world for the last 5,000 years.

…and after the humans are all gone, they will not be missed, not even a little. End of story.

We will be missed. A little at least. Otherwise a few million years of hard work of Mother Evolution would have been in vain. And all the destruction we caused: for nothing. More than just a waste of our potential. What Jon Awbrey’s celestial spheres (comment above) project back is a categorical imperative of cultural evolution: Learn and evolve – You are either a unique occurrence in this universe or all others yet have failed. Thus try not to fail Evolution.

I think we can be fairly confident that the #2 item in the summary will never happen. No material civilisation will ever achieve actual transport at a significant % of light speed or the conversion efficiencies needed to make this plausible, science fiction notwithstanding!

The physics of how to reach near-light speed is actually fairly well understood. Find a pair of orbiting black holes in a highly elliptical orbit and slingshot around the pair repeatedly to build up speed. Because of the geometry of the critical orbit, one can actually slingshot off in any direction in 3-space. You can reach arbitrarily large Lorenz factors this way with little fuel expenditure.

The trick is how to stop once you reach your destination. Hopefully your destination contains a similar pair of orbiting black holes!

In a line of similar thinking with Andrew Robinson, I feel that the idea of aggressively expanding civilizations, while a very clever one, is inherently anthropocentric. ‘Aggressively expanding civilizations’ is one that we have because of history from the past several centuries (one could argue thousands of years), and especially from the last two centuries or so, because of the rise of capitalism coupled with the industrial revolution. But it’s also a limiting view due to our biology.

The issue I see is that we are projecting very sort of ‘human’ ideas onto beings that are, by definition, non-human (if they even exist). Humans are products of their biology; all that human civilization is and has become is, really, just an outgrowth of our primal instincts to survive and reproduce. From the pre-Cambrian times to now, this is how life as we know it on Earth has survived and at times thrived, albeit without the capitalism and Industrialism until recently.

It’s the idea of ‘life as we know it’; what does that phrase even mean? Does it mean another sort of evolutionary history starting with single – celled organisms, or something extremely similar? Does it exclude unconventional life forms with molecular structures that, while similar to ours, were completely unforeseen as being possible to sustain complex & intelligent life?

If something like ‘life on Earth’ were to arise somewhere else, the assumption is that the place will have to be ‘like Earth’. There are many more places that are not like Earth, however, so different versions of ‘life’ that we haven’t even thought of are, in my view, very likely to exist.

Thus far, our ideas of life mean complex sets of molecular structures that sustain themselves (survive) and reproduce themselves for a reasonably long amount of time, because this is what we are, this is all we know.

It’s entirely conceivable that another necessary part of the cycle could be ‘dying’ in a very specific and beneficial way, sort of similar to how some organisms, after mating, have a mechanism in which the female eats the male in order to survive, but this is more primal than that, so that part of the premise of this hypothetical extraterrestrial life tree is based partially on it, in addition to sustaining themselves and reproducing.

And if this specific way of dying, and thus continuing the species’ life cycle, is limited only to the planet or continent where they originated from or to very specific types of planets, then the idea of ‘aggressively expanding civilizations’, as we understand it, is something not only completely foreign to this species, but completely illogical and inconceivable. Like, why would we expand to a planet or move to a hypothetical continent where there are large amounts of a substance that very significantly inhibit our ability to survive, unless we came up with tricks to keep us alive while exploring that? We wouldn’t. We wouldn’t even consider it. It doesn’t make sense, and it can’t ever make sense, because of how we are wired (unless someone is suicidal, but that’s another issue).

It is true that “aggressively expanding civilizations” may seem anthropocentric, but if there are a large number of civilizations in our universe, then no matter how wildly divergent they are, there is some probability that a few will resemble us in this regard. And those are the ones under discussion. And is it really all that anthropocentric? What about insect swarms?

Indeed, I don’t see what’s ‘anthropocentric’ about the idea that some organisms rapidly reproduce, expanding their range until a limiting factor kicks in.

The word ‘aggressive’ is a bit anthropocentric, or at least biased toward the social behavior of certain animals. So, I would not have chosen that word for what’s being studied here.

‘Aggression’ usually connotes the pursuit of resources, or a higher position in a social hierarchy, by damaging or threatening to inflict damage on other agents. So, I would not call the spread of a weed like the morning glory in my back yard ‘aggressive’. Nonetheless it tends to grow rapidly, overwhelming competitors, unless I continually struggle against it.

I would find it surprising if nothing in the Universe behaved in a way like that, once it was able to travel through space.

(As far as I know I wouldn’t have said “corporations” specifically, since I consider this kind of growth a possible feature of evolved life in any form.)

I certainly thought and talked about such things, but I don’t want to take credit for them — such ideas were well-known among the Foresight community, and probably any other community of science fiction fans. The only related “original” ideas I can think of (and even those I would not assume no one else had) were:

an expanding civilization might purposefully create lots of light in order to pre-accelerate surrounding matter into a more accessible frame of reference for eating it (as well as making it less dangerous to collide with);
they might configure the surface and interior of their “bubble” as a large optical telescope (since a telescope is, after all, just a specialized quantum computer using internal interference of light to gain information about incoming light) which could resolve millimeter-sized features about 1000 times farther from them than their bubble’s radius; they have high motive to do so, in order to understand what they’re heading towards — particularly whether it might be about to turn into a competing bubble they might be “about to hit” on their 10^9-year planning timescale. (Since once it does, if it expands at 99.99% lightspeed, its “apparent motion” as they see it approaching will be 10000x faster than that.)
that means that if you stand outside and look at a clear part of the sky (day or night), there’s a reasonable probability you’re visible to a far-away future intelligence. (Wave at them for me, or show them your interesting preprints. They can probably read your lips, having been analyzing everything they can see on Earth since they first noticed life there. Maybe they can even hear you, by seeing the optical wiggling of the background objects behind the sound waves you’re making in the air, or in some other way — I don’t know whether that’s possible. If it is, Earthly intelligences might be doing it too, right now, from satellites.)
being smart and perhaps wise, they won’t necessarily actually want to destroy everything in their path, nor to get into useless wars with the other bubbles they’ll inevitably meet; so if there is any reasonable way to avoid this, it’s very possible they’ll try. The situation may well be understandable and predictable enough to them that they’ll feel confident going a bit slower than maximal due to knowledge or good guesses about what else is around, so maybe they’ll refrain from turning most matter into light and vaporizing everything in their path. They might have the motive of wanting to make a good impression on their future powerful neighbors, or they might even want to adopt a stealthy strategy and spread “invisibly”, or apparently so.

(That post had two normal paragraphs, plus four paragraphs in “bullet point” format, each preceded by a blank line and hyphen. Apparently WordPress ate the blank lines and hyphens, so it now may look like there’s missing text (due to sentences starting with lowercase letters), but I think the actual text is all still there.)

(Chuckle) when such a database finally gets shared with our progeny, some of them may have lots of ‘splainin’ to do.

On the bright side, this presents the distant prospect of definitively resolving some of McEnroe’s disputed line calls, and of finally putting the grassy-knoll theory out to pasture (then again the latter would just morph, wouldn’t it).

By the way: not so long ago, the German bestseller author Andreas Eschbach wrote a well-received book, which I read, about Earth being “contacted” by von-Neumann probes. The title of the Engilsh translation is “The Lord of all things”, literally translated from the German “Der Herr aller Dinge’. I actually forwarded this blog post to Eschbach via G+.

Hi John — thank you for discussing this. One thing that stands out to me is the conception of a “nightmare scenario” vs. a “best possible future.” Both possibilities seem to lead to the same physical picture, on the largest scale.

However, one could also model an in-between “reassuring scenario” similar to what you were imagining back in ’06, where some fraction of the expanders do very little except to “hold” vast regions and resources apart from the others who want to burn it as fuel (though simply holding it does not save it from the eventual expansion and heat death of the universe). As Bruce Smith alluded to above, even an advanced paperclip maximizer run amok probably wouldn’t want to go to war with an equally advanced civilization, as the most likely outcome would seem to be fewer paperclips.

However, one could also model an in-between “reassuring scenario” similar to what you were imagining back in ’06, where some fraction of the expanders do very little except to “hold” vast regions and resources apart from the others who want to burn it as fuel (though simply holding it does not save it from the eventual expansion and heat death of the universe).

This is what I hope happens. One reason is that clever intelligences may be able to think an infinite number of thoughts despite the heat death of the Universe. This was argued by Dyson here:

This is definitely worth reading. Unfortunately it’s a bit outdated because it assumes an open Universe with a vanishing cosmological constant. This gives a temperature that drops to zero as the Universe expands, and I believe this is crucial to Dyson’s argument: as the temperature goes to zero, it takes less and less energy to do interesting things. In the currently popular cosmology, a nonzero cosmological constant makes the universe expand exponentially. In the far future this would create a cosmological horizon with a blackbody temperature of about 10-30 kelvin (analogous to the Hawking temperature of an event horizon). This might prevent future life from thinking infinitely many thoughts. I believe that as a system approaches thermal equilibrium at some nonzero temperature, a machine cannot carry out infinitely many tasks.

Leonard Susskind has pointed out that in thermal equilibrium at any nonzero temperature, any system exhibits random fluctuations. The lower the temperature they smaller these are, but they are always there. These fluctuations randomly explore the space of all possible states of your system. So eventually, if you wait long enough, these random fluctuations will carry the system to whatever state you like. Well, that’s a bit of an exaggeration: these fluctuations can’t violate conservation laws. But conservation of energy doesn’t count here, since at a nonzero temperature, a system is really in a state of all possible energies. So it’s possible, for example, that a ice cube at the freezing point of water will melt or even boil due to random fluctuations. The reason we never see this happen is that such big fluctuations are incredibly rare.

Carrying this thought to a ridiculous extreme, what this means is that even if the universe consists of more or less empty space at a temperature of 10-30 kelvin, random fluctuations will occasionally create atoms, molecules… and even solar systems and galaxies! The bigger the fluctuation, the more rarely it happens—but eternity is a long time. So eventually there will arise, by sheer chance, a person just like you, with memories just like yours, reading a webpage just like this.

However, this is not in contradiction to the observation that as a system approaches thermal equilibrium at some nonzero temperature, a civilization cannot think infinitely many thoughts. A random exploration of all possibilities is not the same as the dedicated pursuit of some line of thought!

Luckily I expect that just as our cosmology changed rather dramatically since Dyson wrote his paper in 1979, the Universe will have many more surprises for us in the eons to come. So, any thoughts about the end should be tentative.

Smolin in his book Time Reborn considers several arguments along these lines. They’re worth repeating here. Eternity is such a long time that, if this process can occur, then it is overwhelmingly likely that our universe is such a fluctuation. But such a fluctuation is overwhelmingly more likely to create a solitary brain with imaginary experiences and memories rather than a complete universe. Therefore if this reasoning holds we should expect that I (for example) am an isolated brain living in a simulated sensory universe. But such simulated universes are overwhelmingly likely to contain inconsistent random garbage. Since we do not perceive inconsistent random garbage, it follows that time cannot be eternal.

This is why I think the statement is wrong even as a plausibility argument:

A well-established scientific theory from two centuries ago explained well which complex structures can be expected to arise in an abundance much higher than suggested by their proportion among all equally weighted configurations: this theory is Darwinian evolution and it refers to self-replicating systems.

Based on this theory I would tend to say that I expect, if I were forced to do so, that the “typical observer in a universe” is a self-replicating system which is a descendant of a very small self-replicating system which arose from some local equilibrium through a comparatively small fluctuation.

And I even have circumstancial experimental support for this statement: by all what we know, the observers that we observe all arose from what must have been a coincidence (=”fluctuation”) by which a bunch of nucleotides suddenly came into an arrangement which lead to self-replication (possibly as described by the RNA world hypothesis).

I find it self-evident that the probability that an observer (a “brain” if you insist) evolves from such a comparatively tiny fluctuation by Darwinian evolution is orders of orders of orders of magnitudes higher than that the observer arises directly by a fluctuation.

I think Smolin does address the Darwinian evolution counter-argument, albeit indirectly, as follows. While evolution may well be the most efficient mechanism for producing (say) life forms starting from a planet Earth orbiting a sun, there is no possible reason why evolution would require a galaxy beyond our own, or even a solar system beyond our own. Therefore it seems that, at one scale or another, small fluctuations (say, at the solar system scale) should be more common than large fluctuations (ones that produce entire universes).

This is what I hope happens. One reason is that clever intelligences may be able to think an infinite number of thoughts despite the heat death of the Universe. This was argued by Dyson here:

That paper by Dyson is one of my all-time favorites. One has to be careful about this sort of motivation/conclusion though. Suppose some variant of Dyson’s approach could work, and that it allows you to think an infinite number of thoughts on any finite reserve of free energy (as Dyson’s approach was originally supposed to).

Then, suppose you build a self-replicating probe with a rational AI and tell it what you value — let’s say “total number of life-thoughts” is one value and maybe you also value “interconnections between life” to some extent. Then, the probe may conclude that the Dyson scheme means that the “total number of life-thoughts” will be in super-abundance, and the correct course of action is to burn almost all resources as quickly as possible, since causal contentedness is rapidly diminishing in an accelerating universe, and we need to do as much living/thinking as possible, while it lasts.

I think that Dyson also wrote a paper presenting a scheme for thinking an infinite number of thoughts in a big-crunch scenario. (Imagine his to-do list from that era: Deal with heat-death fate of universe, check; Deal with big-crunch fate of universe, check; pick up dry cleaning, …)

It looks like I was wrong about Dyson being the author of the infinite-thoughts-in-big-crunch analysis (at any rate, I couldn’t find such a paper by him). Too bad, it would have made a nice bookend for the other.

These conclusions are valid in an open cosmology. It is interesting to examine the very different situation that exists in a closed cosmology. If life tries to survive for an infinite subjective time in a closed cosmology, speeding up its metabolism as the universe contracts and the background radiation temperature rises, the relations (56) and (59) still hold, but physical time t has only a finite duration (5).

Great post! Hannu Rajaniemi wrote about this in the context of Prisoner’s Dilemma in his “Quantum Thief Trilogy”. (Ranajeimi is interesting because he is a Mathematical Physicist in addition to being a hell of a writer. ;)

I do think it has some great possibilities for fiction, for the following reason: We’re probably not very far away from an actual ability to build a probe that could implement something like this — it only takes one self-replicating probe to do it (it has to be fast, smart, self-replicating, and have sufficiently good instructions). Possibly on the order of a single human lifetime from now, depending on how certain technology trends unfold. At the same time, most of the existential risk for humanity (and post-humanity) is concentrated in that same window of time. So it generates a kind of high-stakes race to either the awakening of the local universe, or else permanent destruction, within a human-scale time.

Frank J. Tipler, assuming a forever expanding (and accelerating) universe, thinks that intelligent life will eventualy modify the universe, stopping the acceleration to get a Big Crunch and exist forever, thanks to the Dyson scenario. This could be in some consonance with what professor Baez has commented about civilizations turning matter into radiation and indeed modifying the universe.

I find Tipler’s early book with Barrow interesting, but in his later books The Physics of Immortality and The Physics of Christianity I think he drifts into strange fantasies, which I find uncongenial. But he’s smart, so there are some interesting ideas mixed in with the attempt to reconcile science and Christianity.

I only knew the book “The Physics of Immortality” although I haven’t read it. Perhaps the most surprising claim of the article is where Tipler says that the unitarity in quantum mechanics requires that intelligent life should survive to the end of time.

I don’t believe the laws of physics require intelligent life to survive until the end of the Universe, any more than they require it to have been there at the start or indeed to exist at all. Tipler argues that while an infinite number of universes are logically possible, for them to exist physically they must contain observers to behold and appreciate them. This is his own add-on to the usual laws of physics.

I know two of that theory’s authors, but I didn’t know that theory! (Or else I forgot it.) At first glance it sounds somewhat reasonable, at least if we interpret the voids as “turned-off pointlike emitters” (making their transparency plausible). (Of course that only means (at best) “possible”, not “probable”.)

Astronomers — (1) is there observational evidence that the voids’ matter density (including, of course, of “dark matter”) is in fact less than that of the non-voids? (2) Am I right in assuming that there is observational evidence that the voids are transparent? (I.e. that we see non-void stuff behind them.) (3) Does the “agreed reservations” part of it make sense in terms of possible communication speeds? (4) Are the voids in any sense spherical? (Not that this matters a lot for the theory.)

This idea is fun, but it has immediate problems. The biggest prediction would be a very abrupt and somewhat recent change in the observed density of galaxies in the universe — by a factor of ~10. Then there is the issue that they should still be radiating their waste heat away somehow — where is it? Then there is the issue that genuine voids do have observable consequences — photons from the Cosmic Microwave Background that pass through a void are cooled ever so slightly, and this effect has indeed been observed in the CMB and correlated with the presence of voids. There are probably a bunch of other immediate implications, but this is already a pretty deep hole to climb out of.

Supposing a runaway self-replicating probe with the ability to evolve. I think evolutionary “success” would mean using up all available resources as fast as possible to expand the bubble. Less successful variants would be left “eating their dust” (except there wouldn’t be any dust left so they would die off). So, what if a bubble passed through our galaxy a billion years ago consuming all the dust (and assuming stars and planets were not convenient for them to quickly consume). Can we tell from observation whether this happened?

Nice puzzle! It sounds like your question amounts to: do we know that some the dust in our Galaxy is over a billion years old? All I know for sure is this: the presolar grains in our Solar System are over a billion years old. Many of these grains have become incorporated into meteoroids, but some are still floating around, and some were caught by the Stardust spacecraft in 1999.

How To Write Math Here:

You need the word 'latex' right after the first dollar sign, and it needs a space after it. Double dollar signs don't work, and other limitations apply, some described here. You can't preview comments here, but I'm happy to fix errors.